1. Field of the Invention
The present invention relates generally to pressure control systems for use in an aircraft environment, and more particularly to a cabin pressure control method and apparatus using all electric (electro-mechanical) control without outflow valve, motor speed, or position feedback.
2. Description of the Related Art
Aircraft that fly at high altitudes require a pressurized cabin to allow occupants to safely travel without wearing an oxygen mask. The pressurized cabin is a dynamic environment impacted by the various conditions placed on the aircraft from before take-off to after landing. There are many disturbances to the cabin pressurization such as the changing pressure distribution on the airframe due to ground, taxi, takeoff, landing, or flight maneuvers, or due to changing power in one or more engines that can be a source of pressurized air.
Cabin pressurization systems are of three basic architectures: pneumatic, electro-pneumatic, and all-electric (or electro-mechanical). Until recently, especially for general aviation and regional aircraft, pneumatic and electro-pneumatic systems had the advantage of lighter weight and lower cost than all-electric systems. However, pneumatic and electro-pneumatic systems are mechanically complex in nature, and can often employ motorized bellows, solenoids, torque motors, springs, orifices, and micro valves to control the position of an outflow valve. These systems require bleed air, or a vacuum source, and require tubing to be installed on the aircraft, making their installations more complex, costly, and less reliable. Further, the pneumatic and electro-pneumatic systems typically do not have as wide a dynamic control range relative to all-electric systems. This is because the air that controls these systems must be “pushed” and “pulled” through orifices to and from control chambers that control the valve position.
All-electric cabin pressure systems have many advantages including easier installation on the aircraft (no tubes, vacuum sources, etc.) and a greater dynamic response bandwidth for cabin pressure control when compared with pneumatic or electro-pneumatic systems. However, these all-electric systems were previously quite expensive and heavy because they require sophisticated motor/valve control electronics and motor and/or actuator/valve speed/position feedback to close the control loops. In these systems, the motors would typically have tachometers, hall-effect sensors, resolvers, or some other sensing means of providing feedback to indicate the position of the outflow valve or the amount of aperture opening. In some systems, the outflow valves must have potentiometers, a rotary variable differential transformer (RVDT), which converts angular mechanical displacement into an electrical output, or a linear variable differential transformer (LVDT), which converts linear mechanical displacement into an electrical output to provide valve position feedback. These components can be bulky and expensive.
Low cost aircraft require lower cost and lighter weight cabin pressure control systems to enable aircraft manufacturers to meet level price and performance targets. Further, the smaller aircraft tend to have a smaller pressurized cabin volume, making pressure control even more difficult. Therefore, the conventional approach of using complex pneumatic, or electro-pneumatic pressure control systems is neither efficient nor cost effective, especially when applied to smaller cabin volumes.
Thus, it should be appreciated that there is a need to provide a cost-effective, light-weight, and efficient cabin pressure control system. The present invention fulfills this need as well as others.